Electrochromic glazings include electrochromic materials that are known to change their optical properties, such as coloration, in response to the application of an electrical potential, thereby making the device more or less transparent or more or less reflective. Typical prior art electrochromic devices (hereinafter “EC devices”) include a counter electrode layer, an electrochromic material layer which is deposited substantially parallel to the counter electrode layer, and an ionically conductive layer separating the counter electrode layer from the electrochromic layer respectively. In addition, two transparent conductive layers are substantially parallel to and in contact with the counter electrode layer and the electrochromic layer. Materials for making the counter electrode layer, the electrochromic material layer, the ionically conductive layer and the conductive layers are known and described, for example, in United States Patent Publication No. 2008/0169185, incorporated by reference herein, and desirably are substantially transparent oxides or nitrides.
Traditional EC devices and the insulated glass units (hereinafter “IGUs”) comprising them have the structure shown in FIG. 1. As used herein, the term “insulated glass unit” means two or more layers of glass separated by a spacer 1 (metal, plastic, foam, resin based) along the edge and sealed (seal not depicted) to create a dead air space, “insulated space” (or other gas, e.g. argon, nitrogen, krypton) between the layers. The IGU 2 comprises an interior glass panel 3 and an EC device 4, described further herein.
FIGS. 2 and 3 illustrate plan and cross-sectional views, respectively, of a typical prior art electrochromic device 20. The device 20 includes isolated transparent conductive layer regions 26A and 26B that have been formed on a substrate 34. The EC device 20 includes a counter electrode layer 28, an ion conductive layer 32, an electrochromic layer 30 and a transparent conductive layer 24, which have been deposited in sequence over the conductive layer regions 26. Further, the device 20 includes a bus bar 40 which is in contact only with the conductive layer region 26A, and a bus bar 42 which may be formed on the conductive layer region 26B and is in contact with the conductive layer 24. The conductive layer region 26A is physically isolated from the conductive layer region 26B and the bus bar 42, and the conductive layer 24 is physically isolated from the bus bar 40. Further, the bus bars 40 and 42 are connected by wires to positive and negative terminals, respectively, of a low voltage electrical source 22.
Referring to FIGS. 2 and 3, when the source 22 is operated to apply an electrical potential across the bus bars 40, 42, electrons, and thus a current, flows from the bus bar 42, across the transparent conductive layer 24 and into the electrochromic layer 30. Further, ions, such as Li+ stored in the counter electrode layer, flow from the counter electrode layer 28, through the ion conductive layer 32, and to the electrochromic layer 30, and a charge balance is maintained by electrons being extracted from the counter electrode layer 28, and then being inserted into the electrochromic layer 30 via the external circuit. The transfer of ions and electrons to the electrochromic layer causes the optical characteristics of the electrochromic layer, and optionally the counter electrode layer in a complementary EC device, to change, thereby changing the coloration and, thus, the transparency of the EC device. It is desirable to position the bus bars near the sides of the device 20, where the bus bars, which typically have a width of not more than about 0.25 inches, are not visible or are minimally visible, such that the device is aesthetically pleasing when installed in a typical window frame.
It is often necessary for the bus bar material to extend beyond the IGU seal such that an electrical connection can be made outside the IGU. An internal connection to the transparent conductor layer would, it is believed, compromise the aesthetics of the EC device. Moreover, the typical low temperature bus bar materials employed in the art, e.g. silver-based thick film frit materials, are believed to be porous. As a result, there is believed to be at least a partial leakage of the inert gas stored in the dead air space of the IGU when traditional frit materials are extended outside the IGU under the spacer.
In addition, traditional electrochromic IGU constructions have certain deficiencies with regards to the visual aspect of the bus bars. There is a generally a black obscuration layer around the perimeter of the glass substrates to block the transmission of stray light. However, as seen from the inside, the product fabrication and assembly is such that the shiny silver bus bars can be seen with the black obscuration print in the background. The color difference may be striking and may attract some attention.